The present invention relates to radiation delivery systems, and, in particular, to a radiation delivery balloon in which the radiation source is carried in the wall of the balloon.
Percutaneous transluminal coronary angioplasty (xe2x80x9cPTCAxe2x80x9d) has become an established treatment for occlusive coronary artery disease. A catheter having an inflatable balloon secured to its distal end is advanced through an artery to a narrow region. The balloon is then inflated with a fluid from an external source, causing the narrowed region of the artery to be expanded. The balloon is then deflated and withdrawn. A variety of additional techniques have been developed for restoring patency to a narrowed vessel, including, for example, laser angioplasty and rotational arthrectomy. Although such techniques have enabled a minimally invasive treatment for patients who may otherwise would have been subjected to open heart surgery, long-term follow-up shows that a renarrowing of the vessel or restenosis frequently occurs.
Several studies document a restenosis rate of from about 25% to as much as 35% or more within the first year following PTCA, with the vast majority of patients requiring repeat procedures within six months. In addition, the restenosis rate for angioplasty of the smaller, peripheral arteries also occurs at a significant rate.
Immediate restenosis, also known as abrupt reclosure, results from flaps or segments of plaque and plaque-ridden tissue which are formed during balloon angioplasty and which can block the artery. Such blockage of the artery requires emergency surgery and often results in death. Furthermore, the possibility of an acute reclosure may require that a surgical team stand by during the balloon angioplasty procedure. Restenosis at a later time results from causes that are not fully understood. One mechanism believed responsible for restenosis is fibrointimal proliferation of the stretched wall in which the injured endothelial cells lining the vascular structure multiply and form obstructive fibrous tissue. Fibrointimal proliferation of the vascular wall involves cellular multiplication at a high rate, thereby causing an obstruction to flow through the vascular structure. Often repeat balloon angioplasty or surgery is required, and another episode of restenosis may occur.
At present, there is no effective method for preventing restenosis following angioplasty, arthrectomy, or any of the variety of additional lesser used techniques for restoring patency to a vascular stenosis. However, a variety of techniques have been explored for minimizing restenosis following angioplasty.
For example, a variety of catheters have been devised for delivering heat to the artery wall. See, for example, U.S. Pat. Nos. 4,878,492 and 4,646,737 to Hussein, et al., which are directed to the use of a laser as the heat source.
More recently, exposure of the dilated vascular site to a radioactive source has appeared to show more promise in inhibiting or delaying restenosis. As a consequence, a variety of radiation delivery vehicles have been designed.
For example, radioactive stents and radioactive guidewires are disclosed in U.S. Pat. No. 5,213,561 to Weinstein, et al. A variety of other radioactive catheter structures have also been devised, such as, for example, that disclosed in U.S. Pat. No. 5,199,939 to Dake, et al.
Notwithstanding the various efforts in the prior art to devise an effective radiation delivery system, the systems devised so far contain certain disadvantages. For example, delivery of a uniform dose of radiation circumferentially around the artery is difficult with the radioactive guidewire-type delivery systems, unless the guidewire is centered within the artery such as through the use of a balloon catheter. With the centered guidewire, the radiation dose must be sufficiently high to penetrate the centering catheter and blood or inflation media before penetrating the arterial wall. Radioactive stents may be able to provide a more circumferentially symmetrical delivery of radiation, but removal of an implanted stent is difficult or impossible as a practical matter. Thus, the clinician can exert relatively little control over the dosage delivered through such devices.
Thus, there remains a need for a radiation delivery vehicle for delivering a predetermined dosage of a low energy radiation to a site for a conveniently controllable period of time, for minimizing or delaying restenosis or other proliferative conditions.
There is provided in accordance with one aspect of the present invention a radiation delivery balloon catheter. The catheter comprises an elongate flexible tubular body, having a proximal end and a distal end. An inflatable balloon is provided on the tubular body near the distal end thereof, and the balloon is in fluid communication with an inflation lumen extending axially through the tubular body. A tubular metal foil layer is positioned on the balloon.
Preferably, an outer sleeve surrounds the tubular metal foil layer. In one embodiment, the metal comprises gold, having a thickness of no more than about 0.001 inches. The balloon catheter may be further provided with a perfusion conduit extending axially through the tubular body, in fluid communication with at least one proximal perfusion port on the tubular body on the proximal side of the balloon and at least one distal perfusion port on the tubular body on the distal side of the balloon.
In accordance with another aspect of the present invention, there is provided a multilayer radiation delivery balloon. The multilayer balloon comprises an inner inflatable layer having a radially inwardly directed surface and a radially outwardly directed surface. A radiation delivery layer is provided on the radially outwardly directed surface of the inner layer, and a tubular sleeve is disposed concentrically about the radiation delivery layer, for entrapping the radiation delivery layer against the radially outwardly directed surface of the balloon. In one embodiment, the radiation delivery layer comprises a metal layer, and the tubular sleeve comprises polyethylene terephthalate.
In accordance with a further aspect of the present invention, there is provided a method of treating a site within a vessel. The method comprises the steps of identifying a site in a vessel to be treated, and providing a radiation delivery catheter having an expandable balloon with a continuous annular radiation delivery layer thereon.
The balloon is positioned within the treatment site, and inflated to position the radiation delivery layer in close proximity to the vessel wall. A circumferentially substantially uniform dose of radiation is delivered from the delivery balloon to the vessel wall. The balloon is thereafter deflated and removed from the treatment site.
In accordance with a further aspect of the present invention, there is provided a method of simultaneously performing balloon dilatation of a stenosis in a body lumen and delivering radiation to the body lumen. The method comprises the steps of identifying a stenosis in a body lumen, and providing a treatment catheter having an elongate flexible tubular body with an inflatable balloon near the distal end and a cylindrical radiation delivery layer on the balloon.
The catheter is percutaneously inserted and transluminally advanced to position the balloon within the stenosis, and the balloon is inflated to radially expand the vessel in the area of the stenosis. Simultaneously, radiation is delivered from the metal layer to the vessel wall.
The catheter can be used to deliver radiation to any of a wide variety of sites in a body, such as arteries, veins, intestines, the colon, the trachea, the esophagus, the urethra, ureters, hollow organs, and other cavities, potential cavities and surgically created spaces. Nonmetal radiation carriers can also be used.
Further features and advantages of the present invention will become apparent to those of skill in the art in view of the detailed description of preferred embodiments which follows, when considered together with the attached claims.